Legionnaires disease is a well recognized cause of community acquired pneumonia (CAP) all around the world. In Latin America its incidence remains unknown. This study analyzed a cohort of 9 patients with CAP due to Legionella pneumophila observed from 1997 to 2001, in the Hospital de Clínicas José de San Martín, University of Buenos Aires. Clinical history included recent illnesses, work exposure, physical exam, prior antibiotic use and severity of illness criteria. None of the 9 patients had a history of recent travels, and 4 of them required admission in intensive care unit (ICU). Seven patients had a cigarette smoking history, four of them also had COPD, and one patient had a non-Hodgkin lymphoma. This study confirms the low specificity of clinical and general laboratory criteria to predict this etiology. Legionella isolation is difficult, and serological testing allows retrospective diagnosis but takes several weeks, while urinary antigen test gives a bed-side diagnosis. When Legionella appears in isolated cases, as happens in Argentina, it should be necessary to have a high index of suspicion to successfully arrive at an etiological diagnosis. Legionella pneumophila is a pathogen causing CAP in our area. A surveillance should be established preferably focused on selected populations including severe CAP, immunocompromised hosts and patients with chronic obstructive pulmonary disease.